1. Field of the Invention
The present invention relates to an apparatus for controlling the timing of ignition in an internal combustion engine through detection of knocking induced therein.
2. Description of the Prior Art
In the conventional apparatus of this type known heretofore, it is generally customary to execute a control action through a feedback system where an ignition signal produced at a timing determined on the basis of preset reference ignition timing characteristic is phase-shifted by a fixed angle upon induction of knocking or by a delay angle corresponding to the intensity of knocking and, in case no knock is existent, the amount of such delay-angle phase shift is reduced with a predetermined time constant to control the ignition timing.
In such a control action, however, it is necessary to preset the reference ignition timing ahead of a knock threshold point since the knock suppression control is performed by the use of an angular delay from the reference ignition timing. Therefore, the ignition timing at the control start point is always beyond the knock threshold point, whereby induction of great-intensity knocking is unavoidable. Also in case there occurs any change in the engine running mode, the feedback control quantity related to the previous running mode anterior to such change is applied continuously even after the change, so that a considerable time lag comes to be existent until the control quantity is settled at a desired value which conforms to the post-change running mode. Consequently, the response to a change in the running mode is rendered unsatisfactory. Furthermore, since the controller needs to cover the entire running conditions for knock suppression with the individual feedback control quantities, a wide dynamic range is required and thus it has been difficult heretofore to achieve accurate ignition timing in the entire running conditions.
Induction of knocking is dependent on the performance characteristics of an engine including various factors such as ignition timing, air-to-fuel ratio, suction temperature and suction air humidity. Out of the above factors, those relative to natural phenomena such as temperature and humidity of suction air are in a relatively long variation cycle with respect to the lapse of time like a day or a season, for example. Therefore, generation of knocking derived from any change in such factors also has a long variation cycle. In other words, knocks induced within a short period of time in one engine running mode are substantially the same, and there exists almost no difference among them with respect to the induction frequency or the intensity. That is, the corrective control value required for suppressing the knocks induced in one running mode are substantially the same within a short period of time. Therefore, in one running mode of an engine prescribed by particular running parameters, the corrective control value stored previously is usable as a value for the present stage and, since the ignition timing correction range may be narrow with regard to generation of slight knocking during the control action, high-precision knocking suppression is achievable with an extremely rapid response by executing sequential correction control in response to a knock detection signal at each time of the generation. Moreover, for any change occurring in the aforementioned long-cycle factor, the corrective control value may be altered slowly to carry out the desired correction.
However, if any abnormality such as fault or malfunction is caused, during the running of the engine, in a sensor or an electric circuit provided for detecting the engine vibration, knocking is not detectable and consequently the ignition timing is renewed under control in the direction of angular advance. As a result, the ignition timing fails to be delayed properly at the induction of knocking, hence bringing about the possibility of causing premature ignitions in succession.